In a valuable contribution to the state of the art it is described in the applicant's patent specification DE 197 46 483 how macroscopic quantities of material are ablated, evaporated or melted with micrometer precision in the machining of extensive areas of materials with lasers with a large spot diameter (mm cm) (CO2 lasers, Nd:YAG, excimers, etc.).
In a further valuable contribution to the state of the art, there is described in the applicant's patent specification DE 197 27 573 an algorithm as to how a laser beam can be deflected to ensure the best possible and precise machining of material.
In U.S. Pat. No. 5,656,186, a method for machining material while simultaneously avoiding or minimizing harmful side effects (melt edges, thermal damage, acoustic shock waves, cracking) by choosing a special pulse duration depending on the material.
The material-machining effect of the laser is restricted to a small spatial area of the laser focus (typically some μm3) in which the light intensity is high enough to exceed the threshold of the optical breakdown. Localized to this focus volume, the cohesion of the material is destroyed and a cavitation bubble forms. If the laser focus is guided to a new position for each laser pulse, linear, two-dimensional or three-dimensional cut patterns can be generated. At the end of the machining, the distance between adjacent cavitation bubbles must approximately correspond to the focus diameter so that the material can easily be mechanically detached along the cuts.
Existing laser apparatuses for machining material with femtosecond laser pulses use regenerative amplifiers with which individual pulses of a femtosecond oscillator are amplified. While the oscillator itself provides pulse energies in the nanojoule range only, the pulses can be amplified with a regenerative amplifier up to some millijoules of pulse energy. The repetition rates are limited to some 10s of kHz by using Pockels cells for coupling and decoupling in the amplifier. While these laser sources are suitable for uses with high ablation rates per laser pulse, they are not ideal for the use described above for precision cuts.
In K. König et al., Optics Letters Vol. 26, No. II (2001) it was described how cuts can also be made in tissue with nanojoule pulses from a femtosecond oscillator. However, as a single laser pulse does not lead to the formation of a cavitation bubble, but several pulses positioned at the same point are necessary to achieve a cutting action, this method is suitable only for very fine cut figures on a micrometer scale. This laser source is not suitable for industrial or medical use.